The invention relates to deformable structures for protection of vehicle occupants in particular for direct protection of occupants of a vehicle passenger compartment.
Because of the progressively more stringent vehicle safety requirements, use is made of deformable structures for cushioning arrangements in vehicle passenger compartments. In particular, foams and honeycombs having energy-absorbing properties are provided to reduce the risk of injury or the severity of injuries in the event of an impact because, while maintaining a maximum permissible impact-resisting force, such materials absorb as much kinetic energy as possible and thereby reduce the impact stresses.
Resilient foam materials absorb impact energy up to a certain level and then return the stored energy in the opposite direction. This leads to undesirably high reaction speeds.
Solid plastic foam materials absorb impact energy in the course of the compression of the pores and cells in a satisfactory manner, but only until the cells are completely compressed, leading to a "solid material" condition which produces an excessive increase in impact-resisting force and is not capable of further absorption of energy.
For occupant-protecting energy absorption, it is necessary to achieve a particular force/deformation path characteristic of the deformable element, by which a defined maximum permissible impact-resisting force is not exceeded upon commencement of the deformation, the impact resisting force being maintained over a deformation path which is as long as possible and which substantially corresponds to the thickness of the undeformed deformable element so that the function of the deformable element as an energy absorbing component is preserved and the impact force applied to it is not transmitted in its full magnitude to a vehicle occupant. In order to ensure adequate energy absorption by the deformable element, an excessive increase in impact-resisting force, a so-called force peak, must not occur at the start of the deformation, and the deformation should take place over the entire deformation path at a force level close to, but below the maximum permissible impact-resisting force.
Deformable elements and deformable structures in the form in which they are described in the following prior art documents attempt to provide solutions to this problem.
U.S. Pat. No. 3,989,275 describes a vehicle door having an energy-absorbing cushioning cladding formed as a molded part containing a synthetic, rigid plastic foam with a plurality of molded-on projections, such as ribs, columns or cones, formed on the side remote from a vehicle occupant with a layer of a force-distributing semi-stiff plastic foam disposed on the same side of the cladding as the vehicle occupant compartment.
Deformable structures having energy-absorbing ceramic deformable elements are also known. Thus, German Patent No. 29 17 687 discloses a deformable element which has an energy-absorbing core containing a filling of mineral particulate foams, in particular spherical expanded clay, expanded silicate or expanded slate particles, the volume of which is filled with a foam material, the core being surrounded by a resilient jacket. German Offenlengungsschrift No. 43 40 346 discloses a deformable structure which is made of structured ceramic or framework ceramic embedded in a plastic foam, i.e. a spatial pattern of plastic filaments or plastic lattices. Furthermore, German Offenlengungsschrift No. 43 40 347 describes a beam for motor vehicles which is at least partially filled with a multiplicity of ceramic hollow bodies abutting its inner wall which, when acted upon by a force, become deformed with controlled folding in the direction of the major dimension of the beam. By selecting appropriate ceramic hollow bodies , it is possible to create a coordinated deformation behavior of the beam. In this connection, the use of larger and/or thin-walled hollow bodies provides a longer deformation path, while smaller and/or thicker-walled hollow bodies have a higher capacity to absorb impact forces.
A deformable element made from ceramic hollow bodies of differing diameter and differing wall thickness is described in German Offenlengungsschrift No. 43 40 349. The hollow bodies, preferably hollow spheres of aluminum oxide, are arranged in such a way that those having a relatively large wall thickness and having a greater energy absorption capacity are disposed at the front, on the force application side, and those having a large diameter or a small wall thickness to achieve a greater path length at a lower level of force are disposed behind them with respect to the direction of applied impact force.
The subject of European Application No. 0 530 042 is a vehicle door having a door body containing an impact cushion which is an integral composite structure having an arrangement of mutually parallel elongate foam elements, the axes of which are disposed transversely to the door cladding. U.S. Pat. No. 5,306,066 also describes a vehicle door having an inner and an outer body sheet and having a deformable structure at the inner body sheet which is designed in the form of a honeycomb, the cell-forming walls of which are aligned substantially transversely to the inner body sheet.
In the statement of the prior art in German Patent No. 36 21 697, horizontally disposed tubes or shaped members constructed of a homogeneous material are mentioned as energy-absorbing impact-resisting structures. To improve the specific reshaping capacity of such tubes or shaped members, reinforcement is provided by a tension strap and a compression strap. In this case, the reinforcing elements have cavity-forming elements which are disposed with their longitudinal axes perpendicular to the tension strap and to the compression strap.
Finally, German Patent No. 30 38 252 describes an impact-absorbing deformable element for the knee impact region of a driver and a front seat passenger which is formed from a plurality of tubes extending parallel to each other with the tube axes extending transversely to the direction of impact.
To a greater or lesser extent, limits are set for the above-described arrangements with respect to satisfying the above-mentioned force/deformation path characteristic requirements. In particular, the deformable structure is compressed after a short deformation path and then behaves like a solid material, resulting in an excessive increase in impact-resisting force.